The specific aim of this project is to develop an insert earphone with integrated in-ear sound level calibration capabilities. Insert earphones provide great advantages for hearing testing with a convenient and comfortable way to deliver a stimulus with high noise and intra-aural attenuation. They not surprisingly have become a standard clinical transducer. However, their exact calibration over a wide range of ages from neonates to older adults is questionable due to differences in ear canal volumes ranging from 0.2 to 2 cc. The current use of the same calibration values on such a wide range of populations, significantly limits the effectiveness of calibration, resulting in a wide range of sensation levels for a given ?calibrated? stimulus. A simple and easy way to provide routine in-ear calibration of signals being delivered using insert earphones is necessary in order to standardize clinical testing across populations and clinics. In order to develop the proposed system, the following work will be conducted during Phase I: 1) Develop insert earphone that incorporates a miniature microphone preamplifier and equalizer circuitry in the transducer assembly. 2) Develop a full range of insert earphone disposable tips with a built-in microphone probe tube that can be used for pediatric and adult testing. 3) Develop a stand-alone dual channel microphone amplifier with a Digital Signal Processor (DSP) based hardware and software component usable with any audiometric test system, providing on screen calibration values during testing. 4) Perform a comprehensive bench-mark and validation testing of the system on a wide range of test cavities and stimulus frequencies. The newly developed inserts will be fully compatible with our recently developed USB Jr Duet hardware platform which provides dual built-in microphone amplifiers, allowing immediate integration of the proposed system to current IHS users. A proposed stand-alone dual microphone amplifier component will allow integration with 3rd party audiometric testing devices that use insert earphones, but that do not have the built-in microphone amplifier capabilities. The stand-alone module will provide on-screen calibration measurements concurrently to any other testing application running on the user?s computer. The proposed system will provide an easy to use and integrated approach to in-ear calibration for insert earphones. The device will result in a direct benefit to patients by providing in vivo calibration information that will in turn provide more accurate diagnostic and normative information and result in better patient management with better outcomes. During Phase II, a comprehensive clinical trial is envisioned on a wide range of subjects ranging from neonates to adults, comparing Auditory Evoked Potential (AEP) recordings, Middle Ear Muscle Reflexes (MEMR) and audiometry threshold results, using standard and the proposed in-ear calibration techniques.